Means for eliminating magnetic coupling between coils



March 16 1926. 1,577,421

L. A. HAZELTINE MEANS FOR ELIMINATING MAGNETIC COUPLING BETIBEN COILS Filed April 7, 1924 s She'ets-Shoet 1 1,577,421 L. A. HAZELTINE Mmks FOR amnguxrme MA'GNETIC co'urmqs' BETWEEN COILS Filed April '1, 1924 s sheets-sheet 2 1 Fz'y'. 2c

INVENTOR 1,. A. HAZELTINE usms ma smumuma mmnmc couimm smwsnu cons Filed April 7, 1924 3' Sheets- Sheet 5 INVENTOR Patented Mar.16,1 926. I 1,577,421 UNITED STATES PATENT OFFICE.

LOUIS A. HAZELTINE, OF HOBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR- PORATION; A CORPORATION OF DELAWARE.

MEANS FOR ELIMINATING MAGNETIC COUPLING BETWEEN COILS.

Application filed April 7, 1924. Serial No. 704,629.

To all whom it. may concern:

- Be it known. that I, Louis A. HAZELTINE, a citizen of the United States, residing at No.1024 Hudson Street, Hoboken, in the county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Means for Eliminating Magnetic Coupling Between-Coils; and I do hereby declare clear, and exact description of the invention,sucli as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates systems, particularly quency carrier-current or line-radio systems, employing a plurality. of coils, and has for its object the elimination of undesired mag netic coupling between such coils.

For many electrical. purposes, particularly in radio communication systems, it is common to employ coils each having an open magnetic circuit of non-magnetic material.

Thesim plest and most readily constructed that is, all of its turns are coaxial circles, except for the effect of the winding pitch. The current in such a coil produces a magnetic flux extending a dis tance in all directions and in general linkin with other coils that may be in the neighborhood, thus giving rise tomagnetic the two axes-being at right angles.

' -this cannot'be done coupling between the coils. To avoid such magnetic coupling between two coils it has been customary to mount them with the axis of onelying in the midplane of the other, Three coils can be mounted in this way so that there is no coupling between any two, but with more than three coils because no more than three directions mutually at right ,angles exist in three-di- Further, this method of .to be mounted in a different .manner. A less usual method of avoiding magnetic coupling is to enclose each coil completely in a metal compartment, but this more comlicated construction is usually not desired,

. and the eddy-current loss in the metal walls may be objectionable.

\The pur we of this invention is to arrange a plurality ofcoils-so that all of them may be mounted in a similar manner characterized bythe absence of magnetic .coupling between any two.

the following to be a full-,.

to wave signaling radio and high-free For this purpose the centers of the coils should lie in the same straight line and the axes should be parallel.

It remains, then, to determine the proper angle between each axis and thelline of centers of the coils. This angle has been com puted to be that angle whose tangent is I A more complete understanding of this invention may be had from a consideration of the following description of a preferred embodiment together with the accompanying drawings, in which i Fig. I illustrates the derivation of the coil angle;

Fig. 2 is a top view of an assembled multistage tuned radio-frequency amplifier: Fig. 2 is a front view showing the angle at which the coils of Fig. 2 are placed relative to one another and to their line of centers;

Fig. 2 is a side view showing in detail the structure of one condenser-coil unit taken from Fig. 2%;

Fig. 2 is a diagram of connections employed inthe amplifier illustrated in Fig. 2:

Fig. 3* is a top view of an assembled coupled-circuit regenerative radio receiver to which this invention hasbeen applied;

Fig. 3' is a circuit diagram ofthe connections employed in the regenerative radio receiver shown in Fig. 3, and

' Fig. 4 shows the method of locating the coil angle in Figs. 3 'and 3.

Referring to Fig.1, reference characters L and L denote two coils whose axes are horizontal and in the plane of the drawing where the symbols have the meanings indicated on the figure. The horizontalcomnetic intensity at L, is

ponent of the magnetic intensity at L will then be proportional to d S A(y-i-2x d 2+, 2)5/2 This will evidently be zero when tan 5a;

When the horizontal component of 'the magzero, or, more precisely, the magnetic flux of-L will pass thruL at an effective average angle of 90 to the axis of L,, with the result that no magnetic flux will link with L so there will he no coupling between the coils. The above equation thus gives the desirgl angle 0 as the angle whose tangent is J2, which is approximately 547, or substantially 55. It may be noted'incidentally that this angle is equal to the angle between the diagonal and one edge of a cube. While the above ,derivation applies strictly only when the coils are far apart relative-to their dimensions, yet it has been found by experiment that coils whose axial length is two-thirds their diameter may be brought almost into contact without changing the value of the angle for zero coupling by more than a very few degrees. In particular, when the radial distance between the coils is reduced to one-sixth'their diameter, the angle increases only to '57-; when the radial distance .be-

tween the surfaces is equal to the diameter,

the angle is not distinguishable from the ideal approximate value of (The ratio two-thirds of the axial length to diameter, ives approximately the lowest resistance 'or a single-layer solid-wire coil at high frequency with a given self-inductance and a given' volume occupied by the coil.)

7 In radio-frequency amplifiers, particularly tuned radio-frequency amplifiers, it is desirable and usually necessary to eliminate coupling between the input circuit and the output circuit ofeach vacuum tube. Capac ity coupling may be eliminated by introducing a capacity which neutralizes the coupling capacity of the vacuum tube and connections, as described in my United States Letters Patent Nos. 1,489,228 and 1,533,858. Magnetic coupling between the transformers may conveniently be elimiyes nated in accordance with the present invention by the arrangementillustrated in Figs. 2, 2? and 2. g

Fig. 2 is a top view of a two-stage tuned radio-frequency amplifier and detector showing in particular three transformers T T and T These transformers are shown in elevation in Fig. 2 and the complete diagram of connections is shown' in short connections,

coupling. The

Fig. 2 The secondary coils of these transformers are Wound on insulating cylinders.

'The primary coils of T and T are also wound on insulating cylinders and are placed inside the respective secondaries; T, is made an auto-transformer for convenience. variable condensers connected across them. The primary circuits have relatively small .capacities and the primary coils have usually much fewer turns than the secondary coils, hence the radio-frequency currents in the primary circuit have, a very small magnetic effect as compared with the radio-frequency currents in the secondaries. It is. therefore the secondary coils which particularlyshould have zero magnetic coupling.

Fig. 2 shows the secondary coils, each mounted with an an le of 55 between its axis and the line of centers, thus giving zero magnetic coupling, as explained above. This figure also indicates b at the right that all of th e coils may be similarly arranged when more than two stages of radio frequency are employed. A'

very compact and convenient arrangement results from mounting on the back of each variable condenser its associated transformer, as illustrated in Fig. 2, and in more detail in Fig. 2. This arrangement not only introduces the practical advantages of but thereby also minimizes capacity effects. By thus mounting each coil rigidly to its associated variable condenser, which in turn may be secured to a panel asillustrated in Figs..2 and 2, the coil may be readily placed at'the desired angle, with the assurance that this angle will be permanently maintained.

' In applying this invention, care should be taken to keep masses of metal, particularly All secondary windings are tuned by the dotted coil magnetic metal, and closed electric circuits,

as far as practicable out of fields of the coils, distort the flux the magnetic for these would tend to paths and so cause magnetic each coil mtg have a slight effect on the coil angle.

11 account of unavoidable disturbing features of this sort, it may be desirable to adjust the coil angle finally by experiment. In the amplifier shown in Figs. 2, 2 and 2, this result is attained by setting the coil angle so that the adjustment of the neutralizing capacities O whichgives a zero resultant coupling between stages, is found long, as at short wave lengths; for this result indicates that the capacity coupling is not being called upon to balance magnetic coupling. Experience in making these ad-v justments indicates that for-zero magnetic coupling, this deviation of from its theoretical value of approximately 55 is so slight asusually oopformed by the leads of the 'coil angle to be negligible.

to be the same at 'While the foregoing embodiment of the present invention is exemplified in tuned radio-frequency transformers, it is to be understood that the invention is equally applicable to untuned transformers of radio, or of low-frequency type, or to' any form of I coils between which zero magnetic coupling is desired.

' Another; useful embodimentot this invention is its application to a common form of coupled-circuit regenerative receiver having a tuned rin'1a1-y circuit adjustably coupled with a tuned secondary circuit, the latter circuit being adjustably coupled with a coil in the plate circuit of the detector tube; Such a receiver is illustrated in Figs. 3 and 3", where L is the primary or antenna coil, L, is the coupling coil movable with respect to L L is the main secondary inductance coil, and L; is the plate. coil movable'with respect to L "In order to obtain convenient control of .the

coupling between the primary and second ary circuits, it is desirable to eliminate all capacity couplinglbetween these circuits and I to have all of the magnetic-coupling exist between coils L, and L,., Capacity coupling between the variable condensers C and C is here avoided by 'electrostatically shielding these condensers, as indicated in Fig. 3. Capacity coupling between coils L and L is reduced to a negligible amount by spac-- ing them some distance apart with large grounded conductorsv interposed betweenthe' venient to. mount the coils with their axes alsoat to the axis of rotation of coils' L and L,; for this arrangement permits ofvarying the coupling from-zero to maximum while turning coils L and L through an angle of,18'0, thus giving a fine control of the coupling. The direction of the axes of the fixed coils may be determined as indicated in Fig. at, which represents a tin-rectangular spherical riangle whose corners correspond to the three coordinate axes Y of Fig. 3.

The general. case of zero magnetic coupling between two coils whose dimensions are small in comparison with the distance between them may on occasion be of interest, and the necessary relations will therefore be given If the axes of the .coils' are in the same plane, the condition for zero magnetic coupling is that the 'product'of the tangents of the-angles between the axesand the line of centers shall be equal to 2, the two angles being taken in the same way;

In the special case' when these two angles are equal to each other, making'the axes parallel, this reduces. to the relation that the square of the tangent shall be equal to 2,01 that the tangent itself shall be equal to l2, as discussed previously. ln the most general case when the axes of the two coils are not in the same plane, oneaxis should be projected into the plane containing'thc other axis and'the line of centers. Then the general condition .for Zero magnetic coupling is that the product of the tangents of two angles shall again be equal" to 2, one of these angles being between the second axis and the line of centers and'theot-her being between the projection and the line of centers, both angles being taken in the same way. Iclaim:

' 1. In an electriccoil system comprising a plurality of coils whose length is approxi mately two-thirds the diameter, the method of eliminating undesirable magnetic cou-, pling between the coils thereof, which comprises arranging said coils with their axes parallel and with their'centers on the same straight line and disposing each of said axes at an angle of approximately 55 degrees to the line of centers'of said coils, wherebysubstantially no magnetic flux produced by the'electric current in any of said coilsis inked with any other of said coils. '2. gin electric coil system ,comprising two coils so arranged with relation to each other that the product of the tangent of the angle between the line of centers of said coils and the axis otone ofsald' 0011s and the.

tangent of the angle between the line of centers and theprojection of the axis of the other coil ,upon the plane determined-by the line of centers and the axis of thefir'st'coil,"

is equal to two, the value of said tangents lying between, but not including zero and infinity, said coils being spaced at a di'stanceapart large com ared with the dimensions of the coils w ereby substantially no magnetic flux produced by an electric current ,inone of said coils is linked with the other of said coils.

3. An electric coil system comprising two -eoils,'whose dimensions are small in comparison withthe distance between them' and so arranged with relation to each other that the product :of the tangent of the angle between the line of centers of said coils and the. axis of one otsaid coils and 'the tangent of the angle between the the value of said "tangentsniiying between,

but not including zero and i nity, whereby substantiallyno magnetic flux produced by an electric current in one of saidcoilsis linked-with the other of said coils.

- 4; An electric coil system characterized by the absence of magnetic coupling'between the'coils thereof, which comprises-a plurality of coils arranged Wltll their, centers on the s-a-n'ie straight line and with their axes parallel, said axes being disposed at an angle of approximately a'n'i'degrees to the line of centers of said coils, said coils being spaced such a'distance apart that the magneticitlux producedby any one of the coils will pass thru each other coil at an effective average angle of 90 to the axis'of'said othercoih' '5; An electric coil system characterized by the absence of magnetic coupllng between the coils thereof, which comprises a plurality of non-magnetic core coils arranged lVltll their centers on the same straight line efi'ective average angled-90 to the axis;

of said other coil.

1 6. .An electric coil system characterized by the absence of magnetic coupling between the coils thereof, which comprises aplurality of-coils arranged with their axes in the same plane, each of said axes being 'fiirad'i'e' t am lifier; characterized by the absence of disposed, with i'eference'to the line of centersfof said coils, at that angle whose tangent is" the square" root of two, said coils being-"spaced such 'a distanceapart that the magnetlcJflux produced by anyone of the -coils will passthru' each other coil-at an effectiyleveralgele of 90? to the axis of sa th e v p I -'freq'uency transformer-coupled magnetic coupling. between the transformers aplurality of spaced coils, the

thereof, which comprises an arrangement of the transformers with their centers on the same straight line and with their axes parallel, said axes being disposed, with reference to the line of centers of-said transformers, at that angle whose tangent is the square root of two, said transformers being spaced such a distance apart that the magnetic flux produced by any oneof the transformers will pass thru each other trans-,

former at an effective average angle of 90 to the "axis of said other transformer.

8. In an electric coil system, a plurality of coils arranged in a row, said coils being spaced such a distance apart that the magmon reference line intersecting said coils whereby the magnetic coupling between said coils is reduced to a minimum.

9. In an electric coil system, a plurality of spaced coils arranged in a row, the len of each coil being approximately two-thirds its diameter, the axes of said coils being in the same plane and similarly inclined to a common reference line intersecting said coils whereby the magnetic coupling between said coils is reduced to'a minimum.

10. In an, electric coil system comprising method of eliminating undesirable magnetic coupling between the coils thereof which comprises arranging said coils in a row and with' the axes of the-coils in the same plane, inclining said axes similarly to a common reference line intersecting said coils, and spacing saidcoils at sucha distance apart that the magnetic flux produced by any one of the coils will pass thru each other coil at 'an' effective average angle 0f90 to the axis of said other coil.

7 In testimony whereof I afiix signature.

LOUIS A. HAZELTINE. 

